Petroleum refiners often produce hydrocarbon products, such as turbine fuel, diesel fuel, middle distillates, and gasoline boiling hydrocarbons among others, by hydroprocessing a hydrocarbon stream derived from crude oil or fractions thereof. Hydrocarbon streams that are often subjected to hydroprocessing include vacuum gas oils, heavy gas oils, and other hydrocarbon streams recovered from crude oil by distillation. Conventional hydroprocessing techniques can include, for example, hydrocracking, hydrotreating, hydroisomerization, hydrodesulfurization, and the like. Gasoline boiling hydrocarbons and middle distillates, in particular, are often produced by hydrotreating the hydrocarbon stream, such as vacuum gas oil, to reduce nitrogen and sulfur content of the hydrocarbon stream followed by catalytically hydrocracking the hydrocarbon stream into product hydrocarbons of lower average molecular weight and boiling point. Hydrocracking is conducted under appropriate conditions, including elevated temperature and elevated pressure in the presence of hydrogen, to produce a naphtha stream that includes C4 and C5 isomers, as well as higher boiling hydrocarbons.
Various products can be obtained or derived from the naphtha stream, including components included in gasoline products such as C5+ hydrocarbons as well as C4− hydrocarbons that have other industrial uses. N-butanes present in the naphtha stream are generally separated from the naphtha stream and isomerized to produce isobutane, which is useful as a feed to an alkylation stage to make alkylates or as feed to a dehydrogenation stage to make isobutylene. C5+ hydrocarbons are generally separated from the naphtha stream and fed to a gasoline blending stage for producing gasoline.
Gasoline products generally benefit from elevated octane values and, as such, various isomerized hydrocarbons are generally desired for the gasoline products. However, ethanol is often included in gasoline products and has a higher octane value than many other species present in the gasoline products, thereby reducing the need for other higher octane species in the gasoline products. However, Reid Vapor Pressure (RVP) of the gasoline product is another factor that restricts the components included in the gasoline products.
Isopentane is often a desirable component in gasoline products due to relatively high octane values thereof. However, isopentane has a vapor pressure of about 77 kPa at 20° C., and it would be desirable to include components with lower vapor pressure in the gasoline products to minimize the RVP of the gasoline products. N-pentane has a lower vapor pressure than isopentane, and gasoline products with higher overall C5 hydrocarbon content can be obtained by decreasing isopentane content and increasing n-pentane content while still meeting RVP specifications. Decreased octane values resulting from lower isopentane content in the gasoline products is offset by the ethanol content of the gasoline products. Isopentane content in the gasoline products can be decreased by converting at least some of the isopentane from the naphtha stream into other hydrocarbon species. However, it is undesirable to add additional operating units into existing hydrocarbon processing apparatuses for purposes of converting isopentane and increasing n-pentane yield from the naphtha stream.
Accordingly, it is desirable to provide hydrocarbon processing apparatuses and processes for producing n-pentane and isobutane including conversion of isopentane from the naphtha stream. Further, it is desirable to provide hydrocarbon processing apparatuses and processes that enable conversion of isopentane but that do not require additional operating units. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.